Building block



FIG. 1 is a perspective view of the building block;

FIG. 2 is a side view of FIG. 1, the other side being a mirror image thereof;

FIG. 3 is a top view of FIG. 1;

FIG. 4 is a front view of FIG. 1;

FIG. 5 is a bottom view of FIG. 1; and,

FIG. 6 is a back view of the FIG. 1. 

The ornamental design for a building block, as shown and described. 